Herpes simplex viruses, particularly herpes simplex virus 2, are common sexually transmitted pathogens; recent data indicate that up to 22% of adults in the United States are infected with HSV-2. Genital herpes is not only a serious problem in its own right, but ulcerating lesions caused by this virus are also believed to enhance transmission of HIV. Current antiviral therapy for HSV is directed toward inhibition of DNA replication and reduction of viral production and disease, rather than inhibition of infection. Use of virucidal compounds at the time of contact with an infected individual would not only prevent epithelial infection and replication, but would also prevent neuronal infection and latency. We have tested a number of porphyrin compounds for virucidal activity against HSV-I and HSV-2. Several of the compounds have potent virucidal activity against either HSV-2 alone, or against both HSV-l and HSV-2. At least one of these compounds, GaPPIX, also has activity against several bacterial pathogens, and is nontoxic in mice following intraperitoneal injection (Project 2). We propose to assess the activity and determine the mechanisms of action of the most active of the nontoxic compounds tested to date, as well as other compounds generated in Project l to determine which have the most promise for human use. The specific aims of this project are: l) To measure the virucidal activity of porphyrin compounds in cell culture and in vivo. Each compound will be tested in in vitro assays of virucidal activity and toxicity. Those compounds determined to have the lowest EC9O and/or the fastest rate of inactivation will be further tested in vivo. 2) To determine the growth and pathogenic properties of drug resistant mutants. We will attempt to isolate resistant mutants, both in cell culture and in vivo, and test them for their ability to replicate in cell culture and in several in vivo assays of pathogenesis. 3) To determine the mechanism of action of virucidal porphyrin compounds. We will first determine the stage at which infection is blocked, using assays of virus attachment, penetration, DNA release, and gene expression. Mapping of viral targets will be performed by marker transfer experiments between sensitive and resistant viruses.